1. Field of the Invention
The invention relates generally to semiconductor devices and more particularly to two-terminal diode devices employing offset via holes and methods for manufacturing the same.
2. Description of Related Art
Traditionally, two-terminal semiconductor devices have been packaged using direct via hole metallization. The semiconductor device consists of a diode chip, a semi-insulating substrate having a via hole extending vertically therethrough and a metal heat sink which fills the via hole. The diode chip is located on the metal heat sink, which also serves to ground the diode chip. In the above packaging arrangement, however, etching of the via hole is extremely difficult to control. The diode typically has three layers, wherein the layer adjacent the substrate is only typically 5 microns thick. A via hole must be etched through the substrate to this diode layer without etching this 5 micron thick layer away. Additionally, the metal heat sink is not efficient because of its limited size.
In order to solve the heat removal problem, an enlarged via hole configuration was developed. Since the via hole is increased in size, more metal may be located under the diode which enhances heat transfer efficiency. Unfortunately, parasitic inductance is also increased. Next in the evolutionary process, the integral packaging two-terminal device was developed. The active layer of the diode is placed directly on the heat sink, and the diode and heat sink are embedded in a thick polyimide layer. Because of the low thermal conductivity of the polyimide, heat removal from the diode is not efficient and therefore the device cannot operate for sustained periods of time. Additionally, the packaging is not monolithic because it does not have a semi-insulating substrate, and therefore this packaging scheme is not compatible with monolithic circuits.